As the cost of visible laser diodes drops, their value as a pointing aid will increasingly find new applications in need of the assistance they provide to an apparatus that needs to be visibly aimed. Most notably today, visible lasers are used to aim weapons of all types including personal small arms. Shooters strive to align the visible laser beam with the impact of the projectile at a given range. Such is the effect when aiming a camera and shooting pictures.
Known in the art are cameras that call for the use of a visible laser to assist the photographer in aiming the camera without the need to look through a viewfinder. For example, British Patent No. 2 252 836 discloses a camera/flashlight/laser pointer apparatus used for aiming a camera while in pursuit of a suspicious person. A traditional viewfinder is not needed with this apparatus. In U.S. Pat. No. 5,189,463, a video camera is aimed with the assistance of a visible laser diode that is said to obviate the need for a user to look through a viewfinder.
These devices concentrate a lot of energy into a highly collimated radiation beam of small diameter, and thus can be hazardous to biological tissue if exposed for extended periods. As the visible laser diode has found its way into laser pointers and other consumer goods, the government has found it necessary to classify them by power levels and the potential level of damage where people are concerned. Such is the concern of the above cross-referenced Meyers patent application whereby a visible radiation beam used to aim a camera is broken into multiple discrete beams to avoid impinging all the energy on a human eye.
Laser power control schemes, such as those disclosed in the above cross-referenced McIntyre patent application, take necessary precautions to prevent the intentional or unintentional use of the laser to do damage to the human eye. One of these features is the timing of the overall period that the laser is allowed to be in the "on" mode regardless of the users interaction with the shutter button which triggers the laser. With low power laser diodes, the ability to damage the retina of the eye is a function of the overall power of the beam along with the cumulative effects as a function of time. A second feature is the imposition of an "off" period before the laser can be retriggered which addresses the ability of a reckless person to continue to aim the beam at a subject's eye.
However, the responsible camera user may find these safety measures too constraining. Therefore, it is incumbent upon the camera manufacturer to provide a design that minimizes the risk of tissue damage while maintaining the flexibility of the photographer to follow a moving object. For example, a situation where the safety measures are not necessary includes conditions where the camera is used to track a moving object such as a person running or a race car moving on a track. In these cases, the likelihood that a laser could impinge on the subjects eye for any length of time is extremely low.
Cameras that have this degree of sophistication often include sensing apparatus which warn the user when it detects undesirable camera motion for a given photographic situation. In U.S. Pat. No. 4,448,510 to Makoto, an accelerometer apparatus converts camera shake (movement) into an electrical signal that generates an alarm for notifying the photographer that the possibility of recording blurred images due to camera shake is high. Usually this takes the form of preventing an exposure where the shutter speed is less than 1/(focal length) or forcing the user to either use a lens of appropriately shorter focal length or driving a zoom lens to the equivalent focal length that would minimize the effects of camera shake. Such a camera is described by U.S. Pat. No. 5,365,304 to Hamada et al.
In U.S. Pat. No. 5,386,264 to Sekine et al., a shake detecting device is used to detect the shake of a video signal output from an image sensor and compensate for the movement if it is due to camera shake vs. subject motion. In either case, the detection of relative motion between the camera and the scene would make it virtually impossible to impinge laser light on the retina sufficient to damage biological tissue. Therefore in such conditions, the laser aiming aid should not be turned off in accordance with existing control schemes.